In welding fabrications, the “T” connection or T-joint is one of the most common welded connections used to join two pieces of metal together, in which a first piece of metal such as a stiffener work piece forms the leg of the T and the second work piece is the top of the T. Often, both corners of the T connection are welded with fillet welds, wherein these weld joints are referred to as “dual fillet” welds. In some applications, the joint is long and straight and the welding can be mechanized with a pair of welding torches fixed on a common framework facing both corners of the T connection and both welds are performed concurrently to reduce fabrication time. A common example of dual fillet welding is in the fabrication of girders, in which stiffeners are attached to the web of a girder with two long straight fillet welds. Other examples include T connections on round fabrications, such as connection of stiffeners to a tube or pipe, wherein the tube is rotated and a mechanized welding fixture makes both welds at the corners of the T at the same time. Yet another example of this technology uses a tube as the top of the T and a plate as the leg of the T. In all of these examples, both fillet welds at the corners of a T connection are welded at the same time. Depending on the application, fabricators can use many various arc welding processes including SAW, FCAW-S, FCAW-G, MCAW, or GMAW. With all of the processes listed, the welding procedure (e.g. amps, volts, travel speed, etc.) is closely controlled to achieve the desired weld bead and penetration level. Due to the concurrent welding, however, the high heat and magnetic field from the arc on one side of the joint will often adversely affect the arc and weld puddle on the other side. Typically fabricators are forced to reduce welding procedures to overcome the problems associated with two arcs operating on either side of a T connection. Thus there is a need for improved welding systems and techniques by which high quality welds can be deposited on both sides of a T connection simultaneously.
Other concurrent welding techniques exhibit the same difficulties with respect to the effect of using multiple arcs where one arc adversely affects the other arc. For example, where the work piece is grounded along a common axis, as in a tank welding application, the use of two arcs welding the ends of the tank concurrently often exhibit the same adverse affects. Another example is when two arcs are operating in the same weld puddle along a common line. Again, operating the arcs simultaneously often leads to adverse affects.
As a related issue, in welding such joints, it is difficult to obtain good penetration of the weld. Often, adequate penetration may be achieved but requires multiple passes making the weld somewhat inefficient in terms of the amount of material used and the time and energy necessary to achieve suitable penetration. Therefore, there is a need for improved welding system and technique to achieve better penetration in a T connection or other similar joints.